1. Field of the Invention
The invention is related to the field of rotation sensors and in particular to a vibrating beam rotation sensor.
2. Prior Art
The use of a vibrating reed or cantilever beam to detect a rotational velocity is known in the art. J. Lyman in U.S. Pat. No. 2,513,340 discloses a resiliently mounted electrically driven tuning fork. The vibration of the fork produces periodic changes in its moment of inertia. The periodic changes in the tuning fork's moment of inertia produce periodic forces opposing angular rotation. An angular lag or displacement between the resiliently mounted tuning fork and its base is proportional to the angular or rotational acceleration while the amplitude of the periodic force is proportional to the rotational velocity.
The concept of a single vibrating member is disclosed by Barnaby et al in U.S. Pat. No. 2,544,646. In his angular velocity measuring instrument, two serially connected reeds or cantilever beams are constrained to vibrate at right angles to each other. The first or lower beam is electrically stimulated to vibrate the upper beam. The moment of inertia of the upper beam will produce a periodically varying force resisting an angular displacement from its initial plane of vibration. This periodic force is proportional to the displacement. Rotation of the lower beam will cause the upper beam to vibrate in a plane normal to vibration plane of the lower beam. The vibration amplitude of the upper beam is proportional to the angular velocity of rotation. In two of Barnaby's embodiments, the upper and lower beams are piezoelectric crystals.
Mumme in U.S. Pat. No. 3,842,681 expands Barnaby's vibrating beam concept to a two axis angular rate sensor. In the sensor disclosed by Mumme, the lower vibrating reed is replaced by an oscillating rotary hub. Four cantilever beams are supported from the hub in a cruciform pattern normal to its oscillatory axis and are oscillated as rigid members. Coriolis forces generated by the oscillating cantilever beams oppose the rotation of sensor about one of the axes defined by the cruciform cantilever beam configuration and cause the beams defining the other axis to vibrate in a direction normal to the cruciform plane. The cantilever beams are made from a piezoelectric material which outputs a signal in response to their vibration normal to the cruciform plane.